The present invention relates to a door closing device, and particularly to a door closing device which utilizes a belt-shaped spiral spring to operate a door so that the closing device can be made more compact than the usual one.
Most of the known door closing devices are designed by making use of the elastic restoring force of a coil spring to effect the closing of a door, and usually the regulation and buffering of the closing speed and the working force is controlled by means of a lever or an oil pressure cylinder.
However, when one tries to make a more compact door closing device which utilizes the elastic restoring force of a coil spring, he must use a smaller coil spring. Unfortunately, a small coil spring sometimes does not have sufficient restoring force for closing a door, and therefore, one cannot avoid using a large coil spring for a door closing device, which then results in having to use a larger casing for accommodating the coil spring. Therefore, it is difficult to make the known door closing device more compact.
In addition, a known door closing device also uses a lever or a oil pressure cylinder for regulating and buffering the closing speed and the working force of the coil spring, which is inevitably increases the size of the door closing device. Additional shortcomings of the known door closing device include the fact that the means used for regulating and buffering the closing speed and working force in a liquid operated door closing device is usually complicated, and when the weather is cold, the flowability of the operating liquid may be reduced.